This research seeks to define the role and mechanisms whereby serotonin (5-hydroxytryptamine, 5-HT) affects, or participates in, the control of neuroendocrine systems. Primary attention will be directed to the mechanisms of the hypothalamo-hypophysial gonadotrophic neuroendocrine axis controlling ovulation and related gonadal and reproductive functions. The laboratory rat will be the experimental or subject model animal for most of this work. Most of the focus will be on specific hypothalamic and hypophyseal regions in which serotonergic terminals and/or mechanisms are believed to be physiologically as well as quantitatively prominent. It is believed that improved knowledge concerning these mechanisms and their control wll contribute to new approaches and interventions for optimizing human neuroendocrine and reproductive controls in development, health and disease.